Generally, silver halide emulsion are prepared through the process of forming of silver halide grains by bringing together a soluble silver salt with a soluble halide in an aqueous gelatin solution and then conducting a physical ripening process, a desalting process, and a chemical ripening process of the resulting emulsion. Spectral sensitizing dyes and chemical sensitizing agents are also generally added to the emulsion prior to its utilization in a photographic element.
Tabular silver bromide and bromoiodide emulsions generally have come into use for higher speed color negative and black and white film applications. Formation of these emulsions generally involves a controlled ripening step immediately after nucleation whereby twin planes are formed resulting in tabular crystals which increase in size during the growth step. Such processes have been described in U.S. Pat. No. 4,433,048--Solberg and U.S. Pat. No. 4,439,520--Kofron et al. It is known that various metals such as copper, thallium, lead, mercury, bismuth, zinc, cadmium, rhenium, and group VIII metals such as iron, ruthenium, rhodium, palladium, osmium, iridium, and platinum can be present during precipitation of a silver halide emulsion. Further, it is known that such materials may be added after emulsion formation during sensitization. Reference is made in Research Disclosure 308119, Section I, for listing of metals that may be utilized in emulsion formation. Section 111 of that same disclosure deals with sensitization and also lists a similar group of metals as available for sensitization.
While it has been known that a variety of metals have effect upon silver halide emulsion properties, the use of these metals in ways such as to obtain improved products in a consistent manner remains of interest. It is known that some of these additives will improve reciprocity, but cause a loss in speed. Others may improve speed but cause a loss in long exposure reciprocity properties. Further, the metals sometimes have different properties depending upon where in the emulsion forming or the sensitization process they are added. Further, many of the changes brought about to the properties are dependent upon the quantity of the metal added, as well as when in the forming process it is added. There is a need to determine the most effective ways of using these materials.